This program project outlines a group of studies investigating the basic mechanisms underlying neuronal signalling. A group of six core facilities and six individual projects propose a coordinated, multidisciplinary series of studies on diverse nervous sytems. The core will serve an overall administrative function as well as including centralized data management and analysis, biochemical and electron microscopic instrumentation and electronics and machine shop services. Project 1 will study the mechanisms underlying neuromodulatory control of a completely described neural circuit. Project 2 will study the regulation of mammalian neuronal nicotinic receptors. Project 3 will test the hypothesis that the membranes of radial glial cells upon which the growth cones of embryonic retinal axons travel on their way to the tectum contain factors that support neurite outgrowth. Project 4 will investigate the cellular mechanisms by which leech Retzius neurons change their identity after target contact. Project 5 will test two hypotheses about the molecular modifications of ion channels that occur during embryonic development in Xenopus and Project 6 will study the molecular mechanisms used for signal transduction in Drosophila.